Engineering Enhanced Catalyst Layers Through High Oxygen Permeability Ionomers: A Systematic Study of Material Properties, Processing Parameters, and Performance in PEMFCs

<p dir="ltr">The urgent need to address climate change has accelerated interest in proton exchange membrane fuel cells (PEMFCs) as a promising solution for sustainable transportation and energy systems. However, widespread commercialization faces significant challenges, including high system costs driven by platinum (Pt) catalyst requirements, durability limitations, and performance constraints, particularly in the cathode catalyst layer where efficient oxygen transport is crucial. The ionomer component plays a pivotal role in addressing these challenges, as it influences both proton conductivity and oxygen transport to catalyst sites.</p><p dir="ltr">This thesis investigates the fundamental properties and performance characteristics of high oxygen permeability ionomers (HOPI) in PEMFCs, addressing critical commercialization challenges through five interconnected studies. First, using quasi-free-standing thin films supported on nanoporous substrates, we demonstrate that HOPI exhibits approximately three times higher oxygen permeability compared to conventional Nafion™ D2020, establishing this as a bulk material property rather than an interfacial effect. We then examine crack formation mechanisms in catalyst layers, developing novel image analysis techniques and optimization strategies. While HOPI initially showed higher crack susceptibility than D2020, we establish that optimized processing conditions - including low relative humidity, reduced solids content, and specific ionomer-to-carbon ratios - effectively minimize cracking while maintaining HOPI's performance advantages. A comparative analysis of carbon supports reveals that HOPI performs exceptionally well with both low surface area carbon (LSC) and high surface area carbon (HSC) catalysts, with particularly strong results for LSC systems achieving 68% higher current density at 0.8V compared to D2020, due to optimal interactions with external Pt sites. Even with HSC catalysts, HOPI showed a 12% improvement in current density at 0.8V.</p><p dir="ltr"> Building on these insights, we explore the strategic blending of HOPI with conventional ionomers. A blend containing 25% HOPI not only demonstrates superior performance characteristics, including 27% higher specific activity and 19% higher mass activity compared to pure D2020, but also shows significantly reduced crack formation compared to pure HOPI (reducing crack density from 12% to approximately 5%). This optimal blend achieves enhanced performance while maintaining structural integrity. Finally, through advanced nanoscale X-ray computed tomography analysis, we quantify Pt migration patterns during accelerated stress testing, revealing that HOPI reduces Pt band formation by 21% in LSC systems and 15% in HSC systems, correlating with significantly improved durability metrics. </p><p dir="ltr">These findings provide comprehensive evidence that HOPI technology, when properly optimized, can significantly enhance PEMFC performance, durability, and commercial viability. The research establishes fundamental relationships between ionomer properties, processing conditions, and performance characteristics, while offering practical strategies for implementation in next-generation fuel cell systems. This work contributes to the broader goal of advancing clean energy technologies by addressing key barriers in PEMFC commercialization through innovative materials engineering solutions.</p>